1. Technical Field
The present invention relates to a liquid ejecting apparatus equipped with a liquid ejecting head such as an ink jet printing head, and a control method thereof.
2. Related Art
A liquid ejecting apparatus is an apparatus that includes a liquid ejecting head capable of ejecting a liquid and ejects various types of liquids from the liquid ejecting head. As a typical example of the liquid ejecting apparatus, for example, an image forming apparatus such as an ink jet printer (hereinafter, simply referred to as a printer) that includes an ink jet printing head (hereinafter, simply referred to as a printing head) as a liquid ejecting head and prints an image or the like by ejecting and landing a liquid-drop-shaped ink from a nozzle of the printing head onto a printing medium (ejection target) such as a printing sheet may be exemplified. In recent years, the application of the liquid ejecting apparatus has not been limited to the image forming apparatus, and the liquid ejecting apparatus has been applied to various manufacturing apparatuses. For example, in an apparatus for manufacturing a display such as a liquid crystal display, a plasma display, an organic EL (Electro Luminescence) display, or an FED (Field Emission Display), the liquid ejecting apparatus has been used in order to eject various liquid materials such as a color material or an electrode onto a pixel formation area or an electrode formation area.
The printing head includes a channel unit to which ink is introduced from a liquid storing portion such as an ink cartridge enclosing liquid ink therein and which is provided with a series of liquid channels formed from a reservoir to a nozzle via a pressure chamber or an actuator unit which has a pressure generating element capable of changing the volume of the pressure chamber. In the printing head, the speed of ejecting the ink from the nozzle can be made faster as a variation in the pressure generated by the pressure generating element becomes larger. However, if a larger variation in the pressure is applied to the pressure chamber, a negative pressure occurs when the liquid passes through a diameter-reduced portion of the liquid channels, and hence cavitation occurs due to the negative pressure, which may generate bubbles in the ink. As a result, since a pressure loss is caused by the bubbles mixed with the ink and absorbing a variation in the pressure, so-called dot skipping may be caused when no ink is ejected from the nozzle or a flying path may be curved, thereby causing a problem that ink ejection errors occur in the printing head.
In order to suppress the cavitation causing the ejection errors of the ink, various maintenance processes are carried out. For example, JP-A-2004-243661 discloses a printer capable of suppressing the occurrence of the cavitation due to the negative pressure generated when the pressure chamber is abruptly expanded by providing any one or both of a short driving pulse having a voltage equivalent to that of an expansion pulse before the expansion pulse for deforming the volume of the pressure chamber from the normal state as the reference of a variation in the volume to the expansion state and a short driving pulse having a voltage equivalent to that of a contraction pulse after the contraction pulse for deforming the volume of the pressure chamber from the contraction state to the normal state.
However, in the printer having a configuration in which the potential of the short driving pulse and the potential of the short idle period are changed by a switch, when a difference between the potential of the short driving pulse and the potential of the short idle period is set to be larger, the pressure chamber is abruptly deformed. Due to the abrupt variation in the pressure chamber, it is difficult to reliably suppress the cavitation generated by the negative pressure inside the liquid channel. As a result, the bubbles generated by the cavitation stay inside the liquid channel, and the bubbles absorb a variation in the pressure, thereby causing the problem of the ejection errors.